Preparation and formation mechanism of porous and nanostructured TiO2/BCP coatings on titanium

Porous and nanostructured TiO₂/biphasic calcium phosphate (BCP) composite coatings were prepared on titanium by plasma electrolytic oxidation (PEO). The phase composition, microstructure, thickness and surface roughness of the coatings were characterized. Their formation mechanism were also discussed. The results reveal that the TiO₂/BCP composite coatings mainly consist of anatase, rutile, ß-tricalcium phosphate and hydroxyapatite. The surface of the coatings is porous, rough and nanostructrued with grain diameter of 50-100 nm. A two-step electro-migration mode was proposed to explain the ion migration in electrolyte. The granules consisted of amorphous calcium phosphate compound and the ions in electrolyte were brought onto the coating surface by stirring and electro-migration roles during PEO process, sintered by plasma arc produced locally high temperature surrounding the anode, which accelerated its crystallization. Thus is thought to be the possible mechanism for the TiO₂/BCP composite coatings formation.